Conventional hydrogels are three-dimensional, hydrophilic or amphiphilic polymeric networks capable of taking up large quantities of water. These networks may be composed of various polymers and are insoluble due to the presence of covalent chemical and/or physical crosslinks, such as ionic, hydrophobic interactions or entanglements.
Many conventional hydrogels are severely limited in their application. Some hydrogels are used for pharmaceutical applications such as wound closure, tissue engineering or drug delivery. Hydrogels for tissue sealing are for example disclosed in WO 2008/125655 A1.
Further, WO 99/014259 A1 discloses cross-linked PEG hydrogels in which drug molecules are entrapped.
The release of entrapped drug molecules from such conventional hydrogels depends on the degradation of the hydrogel and may lead to a burst release, temporarily causing too high drug levels and difficult to predict drug release. It is desirable to control and/or sustain the release of the drug from a hydrogel. WO 06/003014 A2 and WO 2011/012715 A1 describe hydrogels as carriers in carrier-linked prodrugs, wherein the biologically active moieties moieties are covalently linked to the hydrogel through reversible prodrug linkers. Such hydrogel-linked prodrugs release the drug controlled and with a specific half-live.
However, the hydrogels disclosed in WO 2011/012715 A1 are preferably used for the controlled and sustained release of smaller drug molecules and may not provide sufficient access for larger drug molecules, such as protein drugs, thus resulting in a low drug load of such hydrogels.